The Philippine Institute of Volcanology and Seismology (Phivolcs) has recorded a total of 3,509 earthquakes in Taal Volcano from Feb. 13 to March 27, 2021, a manifestation of "increased magmatic activity" beneath the restive volcano.
In its 24-hour observation from March 27 to March 28, Phivolcs registered four episodes of volcanic tremor having durations of one to 15 minutes and low-level background volcanic tremor that began at 7:15 p.m. on March 26 until 5:45 a.m. on March 28.
Science and Technology Undersecretary and Phivolcs Officer-in-Charge (OIC) Renato Solidum explained that volcanic earthquakes last less than a minute, while volcanic tremors last more than one minute.
"The volcanic earthquakes and tremor can have typical frequencies of vibration, which can be interpreted as associated with specific volcanic process," Solidum said.
"For example, a harmonic tremor is a volcanic tremor with distinct low frequencies typically associated with movement of magma or gas or both. A low level background tremor is a continuous low energy volcanic tremor. Volcanic earthquakes or volcanic tremor occurrences would have distinct, with beginning and end, and higher energy signals above the low level background tremor," he added.
In the past 24 hours, Phivolcs also continued to observe weak steam emission, rising 20 meters from the Taal Volcano's main crater.
Sulfur dioxide emission averaged 953 tonnes/day last March 27, while temperature highs of 71.8 degrees Celsius and pH of 1.59 were measured from the main crater last March 4 and Feb. 11, respectively.
It added that ground deformation parameters continued to indicate a "very slow and steady inflation and expansion of the Taal region after the January 2020 eruption."
"These parameters may indicate increased magmatic activity at shallow depths beneath the edifice," Phivolcs said.
Taal Volcano will remain under Alert Level 2 due to continuous detection of "increased unrest," it said. Its alert level has been raised from 1 to 2 on March 9.
"Sudden steam-driven or phreatic explosions, volcanic earthquakes, minor ashfall, and lethal accumulations or expulsions of volcanic gas can occur and threaten areas within and around TVI (Taal Volcano Island)," it pointed out.
Phivolcs warned the public from entering the volcano island, which is a permanent danger zone, especially the vicinities of the main crater and Daang Kastila fissure.
Local government units were advised to continuously assess and strengthen the preparedness of previously evacuated barangays around Taal Lake in case of renewed unrest.
Civil aviation authorities were also asked to advise pilots to avoid flying close to the volcano as airborne ash and ballistic fragments from sudden explosions and wind-remobilized ash may pose hazards to aircraft.